Summer heat and growing data center computing power are pushing the world to seek new cooling methods. Scientists from the Karlsruhe Institute of Technology (KIT), together with international partners, analyzed how ready so-called caloric cooling systems are for real-world use - devices that operate without liquid refrigerants (freons) that cause serious harm to the climate. The review was published in the journal Nature Energy.
Traditional refrigerators and air conditioners use compressors and gases that, if leaked, intensify the greenhouse effect. Caloric cooling is based on a different principle: special solid materials heat up under the action of an external field - magnetic, electric or mechanical pressure - and cool down when the effect is removed. This temperature difference can be used to transfer heat, as in an ordinary refrigerator.
According to the German Meteorological Service, June 2026 was marked by a historic heat wave. Global energy consumption for space cooling is expected to more than double by 2050. Additional demand is also being created by the development of artificial intelligence: powerful servers generate a lot of heat and need reliable protection against overheating.
Prototypes of caloric devices are already demonstrating notable successes. Magnetic-field systems have exceeded three kilowatts of power, which takes them beyond purely laboratory experiments and makes them suitable for larger tasks. Mechanically driven samples have surpassed the one-kilowatt mark. Compact devices based on an electric field may find application in electronics or wearable technology.
However, a gap remains between the capabilities of the material itself and the efficiency of the finished device. Heat losses, material fatigue and incomplete use of the cycle's work reduce overall performance. "A material can show large temperature differences in the laboratory," explains the first author of the work, Dr. Kun Wang of the KIT Institute of Microstructure Technology. "But what matters is how efficiently this effect can be used for cooling in a device."
The researchers drew up a roadmap for deployment. The key requirement is durability: devices must withstand millions of cycles in order to operate reliably for years. In addition, they need to absorb and release heat quickly with minimal energy expenditure per cycle.
In the near term, caloric systems will not replace conventional refrigerators everywhere. "At first they will be of interest where traditional cooling is approaching practical limits," says group leader Dr. Jingyuan Xu. "For example, when devices must operate very quietly or when refrigerants with high global warming potential must be avoided." Standardized tests and application-oriented demonstrators will show which systems are suitable for these tasks.